Die attached to a support member by a plurality of adhesive members

ABSTRACT

Methods and systems for adhering microfeature workpieces to support members are disclosed. A method in accordance with one embodiment of the invention includes disposing a first adhesive on a surface of a microfeature workpiece, and disposing a second adhesive on a surface of a support member. The method can further include adhesively attaching the microfeature workpiece to the support member by contacting the first adhesive with the second adhesive while the second adhesive is only partially cured. In further particular embodiments, the first and second adhesives can have different compositions, and the second adhesive can be fully cured after the microfeature workpiece and support member are adhesively attached.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/053,984 filed Feb. 8, 2005, now U.S. Pat. No. 8,278,751, and isrelated to U.S. application Ser. No. 11/407,560 filed Apr. 19, 2006, nowU.S. Pat. No. 7,518,237, each of which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present invention relates generally to methods and systems foradhering microfeature workpieces to support members.

BACKGROUND

Packaged microelectronics assemblies, such as memory chips andmicroprocessor chips, typically include a microelectronic die mounted toa substrate and encased in a plastic protective covering. The dieincludes functional features, such as memory cells, processor circuitsand interconnecting circuitry. The die also typically includes bond padselectrically coupled to the functional features. The bond pads areelectrically connected to pins or other types of terminals that extendoutside the protective covering for connecting the die to buses,circuits, and/or other microelectronic assemblies.

In one conventional arrangement, the die is mounted to a supportingsubstrate (e.g., a printed circuit board), and the die bond pads areelectrically coupled to corresponding bond pads of the substrate withwire bonds. After encapsulation, the substrate can be electricallyconnected to external devices. Accordingly, the substrate supports thedie and provides an electrical link between the die and the externaldevices.

Prior to encapsulation, the microelectronic die is typically attached tothe substrate with an adhesive. For example, one conventional assemblyincludes a wafer backside laminate (WBL) that adheres themicroelectronic die to the substrate. Other assemblies include an epoxythat adheres the microelectronic die to the substrate. The foregoingadhesion techniques have both advantages and drawbacks. For example, aWBL generally increases the strength of the die, but does not fill insurface features on the substrate. Accordingly, the bond formed betweenthe die and the substrate may fail due to an inadequate adhesive bond.Epoxies tend to flow more than WBLs do and can accordingly fill suchfeatures, but epoxies can fail in shear at the junction between theepoxy and the die, and/or at the junction between the epoxy and thesubstrate. Accordingly, it is desirable to adhere dies to substrates ina more robust manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a microfeature workpiece having a first adhesive inaccordance with an embodiment of the invention.

FIGS. 2A-2F illustrate a process for manufacturing a microfeatureworkpiece assembly using first and second adhesives in accordance withan embodiment of the invention.

FIG. 3 is a partially schematic illustration of a microfeature workpieceattached to a support member in accordance with another embodiment ofthe invention.

FIG. 4 is a partially schematic illustration of a support membercarrying two microfeature workpieces in accordance with anotherembodiment of the invention.

FIG. 5 is a partially schematic illustration of a support membercarrying two microfeature workpieces in accordance with still anotherembodiment of the invention.

DETAILED DESCRIPTION

The present invention relates generally to microfeature dies and methodsfor adhering such dies to support members, for example, printed circuitboards. A method for attaching a microfeature workpiece to a supportmember in accordance with one aspect of the invention includes disposinga first adhesive on a surface of the microfeature workpiece anddisposing a second adhesive on a surface of the support member. Themethod can further include adhesively attaching the microfeatureworkpiece to the support member by contacting the first adhesive withthe second adhesive while the second adhesive is only partially cured.For example, the method can include attaching a film adhesive to themicrofeature workpiece, and stenciling a liquid epoxy on the supportmember. The method can further include partially curing the epoxy (forexample, to B-stage) before attaching the microfeature workpiece to thesupport member by contacting the two adhesives with each other. Themethod can include further curing the second adhesive to complete thebond between the microfeature workpiece and the support member.

In particular embodiments, the microfeature workpiece can have a firstmajor surface, a second major surface facing opposite from the firstmajor surface, and an edge surface between the first and second majorsurfaces. The method can further comprise electrically coupling thesupport member to the microfeature workpiece at the second major surfaceof the workpiece. In still a further aspect of the invention, themicrofeature workpiece can be attached to the support member withouteither the first adhesive or the second adhesive contacting the edgesurface of the microfeature workpiece.

A method in accordance with another aspect of the invention includesstiffening a microfeature workpiece by disposing a first adhesive layeron a surface of the microfeature workpiece, with the first adhesivelayer having a first composition. The method can further include fillingvoids in a surface of a support member by disposing a second adhesivelayer on a surface of the support member, with the second adhesive layerhaving a second composition different than the first composition. Themethod can still further include adhesively attaching the microfeatureworkpiece to the support member by contacting the first adhesive layerwith the second adhesive layer.

Other aspects of the invention are directed toward microfeatureworkpiece systems or assemblies. A system in accordance with one aspectof the invention includes a microfeature workpiece having a first majorsurface, a second major surface facing away from the first majorsurface, and an edge surface between the first and second majorsurfaces. The system can further include a support member positionedadjacent to the microfeature workpiece, and an adhesive assemblyattached between the microfeature workpiece and the support member. Theadhesive assembly can include a first layer having a first compositionand a first generally uniform thickness, a second layer having a secondcomposition different than the first with a second generally uniformthickness. In further specific aspects, the adhesive assembly can begenerally out of contact with the edge surface of the microfeatureworkpiece, and the microfeature workpiece can be electrically coupled tothe support member with an electrical coupling connected between thesupport member and the second major surface of the microfeatureworkpiece.

FIG. 1 is a partially schematic, cross-sectional side view of amicrofeature workpiece 110 that can be attached to a support member toform an assembly (e.g., a package) in accordance with an embodiment ofthe invention. The microfeature workpiece 110 can have a first majorsurface 111, a second major surface 112 facing generally opposite fromthe first major surface 111, and an edge surface 113 between the firstand second major surfaces 111, 112. The microfeature workpiece 110 caninclude a microelectronic die that has been separated from a largersubstrate, e.g., a semiconductor wafer. The microfeature workpiece 110can accordingly include internal microelectronic features and structures(not visible in FIG. 1) that are electrically coupled to workpiece bondpads 114. The bond pads 114 can provide for electrical communicationbetween features and structures within the microfeature workpiece 110,and components and structures external to the microfeature workpiece110.

The microfeature workpiece 110 can include a first adhesive 115adhesively attached to the second surface 112, and configured to bondthe microfeature workpiece 110 to a support member. In one embodiment,the first adhesive 115 can include a wafer backside laminate (WBL) thatis applied to the microfeature workpiece 110 at the wafer level (e.g.,before the microfeature workpiece 110 is separated or diced from alarger wafer or other substrate). For example, a sheet of the firstadhesive 115 can initially be carried by a dicing frame and attached toa wafer. The wafer attachment process can occur at an elevatedtemperature (e.g., 40° C.-80° C.) and/or pressure (e.g., 20-50 psi).After dicing the wafer, a small portion of the first adhesive 115remains attached to each microfeature workpiece 110, and a standard pickand place process can be used to move the microfeature workpiece 110.The first adhesive 115 can include a film substrate having adhesivematerial attached to both opposing surfaces of the film (e.g., adouble-backed adhesive film). In another embodiment, the first adhesive115 can be a monolayer, e.g., a single layer of adhesive applied to thesecond surface 112 of the microfeature workpiece 110. Suitable firstadhesives are available from Ablestick Laboratories of Rancho Dominguez,Calif. under part number RP787-3DS, and from the Hitachi ChemicalCompany Ltd. of Tokyo, Japan under part number FH-800.

The first adhesive 115 can act not only to adhere the microfeatureworkpiece 110 to a support member, but also to stiffen the microfeatureworkpiece 110. As a result, the microfeature workpiece 110 can be lesslikely to break during normal handling operations. This can beparticularly important for very thin microfeature workpieces 110, whichmay be more susceptible to such breakage. Such microfeature workpieces110 can have a thickness of 150 microns or less, e.g., 100 microns orless.

FIGS. 2A-2F illustrate a support member 220 and a method for attachingthe support member 220 to the microfeature workpiece 110 described abovewith reference to FIG. 1. Beginning with FIG. 2A, the support member 220can include a printed circuit board or other suitable structure havingprovisions for electrical connections to the microfeature workpiece 110(FIG. 1). For example, the support member 220 can include first bondpads 221 at a first surface 227, second bond pads 222 at an opposite,second surface 228, and internal conductive structures (not visible inFIG. 2A) coupling the first bond pads 221 to the second bond pads 222.In preparation for applying an adhesive to the support member 220, astencil 223 can be positioned adjacent to the first surface 227. Thestencil 223 can include one or more openings 224 sized in accordancewith the desired attachment surface area between the support member 220and the microfeature workpiece 110.

Referring next to FIG. 2B, a second adhesive 225 can be applied to thesupport member 220 in a stenciling process. Accordingly, the secondadhesive 225 can be distributed over the stencil 223 using techniqueswell-known to those of ordinary skill in the relevant art to fill theopening 224. In one aspect of this embodiment, the second adhesive 225can include an epoxy that is applied to the support member 220 when in aliquid or otherwise generally flowable state. Accordingly, the secondadhesive 225 can readily fill the opening 224 in the stencil 223. Thesecond adhesive 225 can also readily fill gaps, recesses, projections,roughness elements, and/or other surface features 229 in the firstsurface 227 of the support member 220. As a result, the second adhesive225 can be in intimate contact with the surface features 229 to providea robust bond with the support member 220.

In FIG. 2C, the stencil 223 is removed and the second adhesive 225 canbe partially cured. The process of partially curing the second adhesive225 can include applying heat 226 and, optionally, pressure, to thesecond adhesive 225. For example, the temperature of the second adhesivecan be elevated to about 100° C. for about one hour, at atmosphericpressure, in an inert (e.g., nitrogen) environment. When the secondadhesive 225 includes an epoxy, the partial curing process shown in FIG.2C can include forming a B-stage epoxy. As used herein, the term“B-stage” includes, but is not necessarily limited to, an intermediatestage in the reaction of a thermosetting resin in which the materialsoftens when heated and swells when in contact with certain liquids, butdoes not entirely fuse or dissolve. In this stage, the second adhesive225 is generally non-tacky (e.g., tack-free). Suitable epoxies includeSumitomo X2225 available from Sumitomo Electric Industries, Ltd. ofOsaka, Japan, and Ablestik RP809-1A available from Ablestik Laboratoriesof Rancho Dominguez, Calif.

Referring next to FIG. 2D, the microfeature workpiece 110 can bepositioned proximate to the support member 220, with the first adhesive115 of the microfeature workpiece 110 facing toward the second adhesive225 of the support member 220. The microfeature workpiece 110 and thesupport member 220 can be moved toward each other so that the firstadhesive 115 contacts the second adhesive 225. The local temperature canbe elevated (e.g., up to 100° C.-150° C.) for 1-3 seconds to “re-tack”the first and second adhesives 115, 125. The local pressure can also beelevated (e.g., by from about 1 g/mm² to about 8 g/mm²) in a standardair environment. FIG. 2E illustrates the microfeature workpiece 110 withits first adhesive 115 contacting the second adhesive 225 of the supportmember 220. At this point, the second adhesive 225 can be fully cured byapplying heat 226 (and optionally, pressure) to the second adhesive 225to form an adhesive assembly 230 that includes both the first adhesive115 and the second adhesive 225. In one embodiment, the adhesiveassembly can be cured at 100° C.-150° C. for 1-2 hours in an inertenvironment. The resulting combination of the microfeature workpiece110, the support member 220, and the adhesive assembly 230 forms anoverall assembly or system 200 (e.g., a microfeature package).

Referring next to FIG. 2F, the assembly 200 can include electricalcouplings between the microfeature workpiece 110 and the support member220. For example, the assembly 200 can include wirebonds 201 extendingbetween the workpiece bond pads 114 and the first bond pads 221 of thesupport member 220. The assembly 200 can optionally include anencapsulant 202 that at least partially surrounds the microfeatureworkpiece 110 and the wirebonds 201 or other electrical couplingsbetween the microfeature workpiece 110 and the support member 220. Thecompleted assembly 200 can be electrically coupled to other componentsvia the second bond pads 222 located at the second surface 228 of thesupport member 220.

One feature of embodiments of the assembly 200 described above withreference to FIGS. 1-2F is that they can include multiple adhesives. Afurther particular feature of at least some of these embodiments is thatan adhesive having a first composition can be positioned adjacent to themicrofeature workpiece 110, and an adhesive having a second, differentcomposition can be positioned adjacent to the support member 220. Thiscombination of adhesives can provide one or more of several advantages.For example, the first adhesive 115 can stiffen and strengthen themicrofeature workpiece 110 and can accordingly reduce or eliminate thetendency for the microfeature workpiece 110 to warp, chip, and/or deformin other manners. Preventing the microfeature workpiece 110 from warpingcan be particularly important for workpieces 110 having high aspectratios, e.g., about 4:1, 5:1 or up to 10:1. The second adhesive 225, onthe other hand, can more readily fill in the surface features 229 of thesupport member 220. Accordingly, the second adhesive can be less likelyto leave air voids or other imperfections that may reduce the bondstrength between the second adhesive 225 and the support member 220.

Another feature of at least some of the foregoing embodiments is thateach of the adhesive layers can have a generally uniform thickness. Forexample, the first adhesive 115 can have the form of a generally uniformfilm. The second adhesive 225 can be applied with a generally uniformthickness by using the stencil 223. Because each adhesive layer has agenerally uniform thickness, the microfeature workpiece 110 will be lesslikely to be tilted relative to the support member 220. An advantage ofthis arrangement is that it can reduce the likelihood for themicrofeature workpiece 110 (and/or the wirebonds 201) to be exposedthrough the encapsulant 202 as a result of the microfeature workpiece110 being tilted or otherwise misaligned relative to the support member220.

Another feature associated with embodiments of the generally uniformlayer thicknesses described above is that the adhesive assembly 230 canbe attached directly between the support member 240 and the secondsurface 112 of the microfeature workpiece 110, without extending alongthe edge surfaces 113 of the microfeature workpiece 110. An advantage ofthis “fillet-less” arrangement is that the adhesive assembly 230 may beless likely to subject the edge surfaces 113 of the microfeatureworkpiece 110 to stresses that can crack or otherwise damage themicrofeature workpiece 110.

Still another advantage of at least some of the foregoing embodiments isthat the adhesive assembly 230, formed from adhesives having differentchemical constituencies, can form a tight bond with both themicrofeature workpiece 110 and the support member 220. When subjected toexcessive stresses, the failure mode of the adhesive assembly 230 can becohesive rather than adhesive. For example, the adhesive assembly 230can fail internally rather than at the interfaces between the adhesiveassembly 230 and either the microfeature workpiece 110 or the supportmember 220. Because higher stresses are typically required for failurein the cohesive mode than in the adhesive mode, the overall strength ofthe bond between the support member 220 and the microfeature workpiece110 can be greater than it is for existing adhesive arrangements.

Yet another feature of the foregoing embodiments is that the adhesiveassembly 230 can produce a bond that more readily withstands typicalmoisture sensitivity testing environments. Such environments typicallyinclude transitions in temperature up to about 260° C., and an elevatedhumidity. Improved moisture sensitivity can also result in lower packagestresses in challenging environmental conditions. As a result of any ofthe foregoing features, the package 200 can be more robust than existingpackages, and can accordingly be more reliable in a wider variety ofapplications.

Methods and adhesive assemblies at least generally similar to thosedescribed above with reference to FIGS. 1-2F can be used to bondmicrofeature workpieces to support members in other configurations aswell. Referring now to FIG. 3, a microfeature workpiece assembly 300 caninclude a microfeature workpiece 310 having centrally located workpiecebond pads 314 in accordance with another embodiment of the invention. Acorresponding support member 320 can include an aperture 331 alignedwith the workpiece bond pads 314. The first adhesive 115 can bepositioned adjacent to the microfeature workpiece 310 (outwardly fromthe workpiece bond pads 314), and the second adhesive 225 can bepositioned adjacent to the support member 320 (outwardly from theaperture 331). After the second adhesive 225 has been partially cured,the microfeature workpiece 310 can be bonded to the support member 320using a second curing process. The workpiece bond pads 314 can then beelectrically coupled (e.g., with wirebonds 301) to first bond pads 321of the support member 320. The resulting connection can be at leastpartially surrounded with an encapsulant 302. The first bond pads 321can be electrically coupled to second bond pads 322, which can in turnprovide communication with other devices, for example, via solder balls303.

FIG. 4 illustrates a microfeature workpiece package or assembly 400 thatincludes two microfeature workpieces 410, shown as a first microfeatureworkpiece 410 a and a second microfeature workpiece 410 b. The firstmicrofeature workpiece 410 a can be adhesively secured to a supportmember 420 with a first adhesive assembly 430 a. The first adhesiveassembly 430 a can include a first adhesive 115 and a second adhesive225, configured in a manner generally similar to that described above.The second microfeature workpiece 410 b can be adhered directly to thefirst microfeature workpiece 410 a with a second adhesive assembly 430 bthat also includes a portion of the first adhesive 115 and the secondadhesive 225. First wirebonds 401 a can electrically couple the firstmicrofeature workpiece 410 a to the support member 420, and secondwirebonds 401 b can electrically couple the second microfeatureworkpiece 410 b to the support member 420. The entire package 400 can besurrounded by an encapsulant 402.

In one aspect of an embodiment shown in FIG. 4, the first microfeatureworkpiece 410 a can have a configuration generally similar to that ofthe second microfeature workpiece 410 b, and the second microfeatureworkpiece 410 b can overhang the first microfeature workpiece 410 a toallow for electrical coupling to both microfeature workpieces. In otherembodiments, multiple microfeature workpieces can be stacked in otherconfigurations. For example, referring now to FIG. 5, a package 500 caninclude a first microfeature workpiece 510 a and a second, smallermicrofeature workpiece 510 b, stacked upon the first microfeatureworkpiece 510 a. This arrangement allows bond pads 514 on the outeredges of each microfeature workpiece 510 to remain exposed despite theadhesive connection between the two microfeature workpieces. The firstmicrofeature workpiece 510 a can be secured to a support member 520 witha first adhesive assembly 530 a, and the second microfeature workpiece510 b can be secured to the first microfeature workpiece 510 a with asecond adhesive assembly 530 b. Each adhesive assembly 530 a, 530 b caninclude the first adhesive 115 and the second adhesive 225. In otherembodiments, arrangements generally similar to those described above canbe used to attach one or more microfeature workpieces to correspondingsupport members and/or other microfeature workpieces.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. For example, the microfeatureworkpiece can be electrically coupled to a corresponding support memberwith an electrical link other than a wirebond. Aspects of the inventiondescribed in the context of particular embodiments may be combined oreliminated in other embodiments. Although advantages associated withcertain embodiments of the invention have been described in the contextof those embodiments, other embodiments may also exhibit suchadvantages. Additionally, none of the foregoing embodiments neednecessarily exhibit such advantages to fall within the scope of theinvention. Accordingly, the invention is not limited except as by theappended claims.

We claim:
 1. A microfeature workpiece assembly, comprising: amicrofeature workpiece including a microelectronic die, the microfeatureworkpiece having a first major surface, a second major surface facingaway from the first major surface, and an edge surface between the firstand second major surfaces; a support member having a support surfacefacing toward the second major surface of the microfeature workpiece; anadhesive structure including a wafer backside laminate directly attachedto the second major surface at a first interface, the wafer backsidelaminate including a film substrate having opposing major surfaces andadhesive material attached to both of the opposing major surfaces, andan adhesive layer directly attached to the support surface of thesupport member at a second interface; and an electrical couplingextending between the microfeature workpiece and the support member,wherein the wafer backside laminate and the adhesive layer are distinctstructures bonded to one another, and the adhesive structure isconfigured to preferentially fail at a location between the first andsecond interfaces.
 2. The assembly of claim 1 wherein the adhesive layeris infiltrated into surface features of the support surface of thesupport member to a greater extent than the wafer backside laminate isinfiltrated into surface features of the second major surface of themicrofeature workpiece.
 3. The assembly of claim 1 wherein the waferbackside laminate is directly attached to the adhesive layer.
 4. Theassembly of claim 1 wherein the adhesive structure is out of contactwith the edge surface.
 5. The assembly of claim 1 wherein a failure modeof the assembly between the second major surface of the microfeatureworkpiece and the support surface of the support member is cohesive. 6.The assembly of claim 1 wherein the adhesive layer is configured toinfiltrate surface features of the support surface.
 7. The assembly ofclaim 6 wherein the adhesive layer includes an epoxy.
 8. The assembly ofclaim 1 wherein the adhesive layer is in a stenciled pattern on thesupport surface of the support member.
 9. The assembly of claim 1wherein the wafer backside laminate is flat.
 10. The assembly of claim 9wherein the adhesive layer is flat.
 11. The assembly of claim 1 whereinthe electrical coupling is a wire bond.
 12. A microfeature workpieceassembly, comprising: a microfeature workpiece including amicroelectronic die, the microfeature workpiece having a first majorsurface, a second major surface facing away from the first majorsurface, and an edge surface between the first and second majorsurfaces; a support member having a support surface facing toward thesecond major surface; an adhesive structure directly attached to thesecond major surface via a first bond and directly attached to thesupport surface via a second bond, the adhesive structure including aninternal bond positioned between the first and second bonds, theinternal bond being weaker than the first bond and weaker than thesecond bond, a double-backed film adhesive positioned toward themicrofeature workpiece, and a flowable adhesive positioned toward thesupport member; and an electrical coupling extending between themicrofeature workpiece and the support member.
 13. The assembly of claim12 wherein the internal bond is a cohesive bond.
 14. The assembly ofclaim 12 wherein the adhesive structure is out of contact with the edgesurface.
 15. The assembly of claim 12 wherein the flowable adhesive isin a stenciled pattern on the support surface.
 16. The assembly of claim12 wherein the electrical coupling is a wire bond.
 17. A microfeatureworkpiece assembly, comprising: a microfeature workpiece including amicroelectronic die, the microfeature workpiece having a first majorsurface, a second major surface facing away from the first majorsurface, and an edge surface between the first and second majorsurfaces; a support member having a support surface facing toward thesecond major surface; an adhesive structure including a first layerdirectly attached to the second major surface via a first bond, a secondlayer directly attached to the support surface via a second bond, and aninternal bond positioned between the first and second bonds, theinternal bond being weaker than the first bond and weaker than thesecond bond; and a wire bond extending between the microfeatureworkpiece and the support member, wherein the first and second layershave different chemical compositions, and the first and second layersare directly bonded to one another via the internal bond.
 18. Theassembly of claim 17 wherein the second layer is infiltrated intosurface features of the support surface to a greater extent than thefirst layer is infiltrated into surface features of the second majorsurface.
 19. The assembly of claim 17 wherein: the first layer includesa portion of a wafer backside laminate; and the second layer includes anepoxy.
 20. The assembly of claim 17 wherein the second layer is in astenciled pattern on the support surface.